The invention relates to an electrophotographic process and particularly to an electrophotographic process for forming a plurality of duplicated copies having the same image by repeating development and transfer steps successively for an electrostatic charge latent image once formed on an electrostatic charge retentive member.
Such an electrophotographic process has been known and described in Japanese Patent Application Publication Nos. 7,789/71 and 17,298/74. In the former publication there is disclosed a technique for avoiding a discharge phenomena which might be produced when a record paper is separate from a photosensitive member after a latent image has been developed with toner particles by means of a cascade development method and the toner image has been transferred to the record paper by means of an electrostatic transfer step with using a corona charger. In the later publication there is described a method for reducing a decay in potential of the electrostatic charge latent image by applying a magnet brush development method with the aid of magnetic carriers having coated with an electrically insulating surface layer. In these known processes since an edge effect is liable to appear during the development step it is necessary to arrange an electrically conductive development electrode in proximity of the latent image and in order to avoid an overdevelopment of the base or background in the image it is necessary to apply a development bias voltage to the development electrode. Therefore during the development the electrostatic charge forming the latent image escapes or leaks by means of the developer particles and the development electrode so that the potential of the latent image is decreased and thus it is impossible to print a number of copies of high quality from the single and same charge latent image. Particularly in a high humidity condition the development particles become damp and thus the potential of the latent image might be decreased to a greater extent. Further in case of using the magnetic carriers having insulating surface it is quite difficult to make such carriers having the high resistance and the mechanical strength of the insulating coats is rather low. Therefore the potential of the electrostatic charge latent image could not be sufficiently maintained articularly in the high humidity condition.